Rio de Janeiro, Aug 20 (Reuters) - Brazilian security forces in Rio de Janeiro on Tuesday morning shot dead a man who hijacked a commuter bus on a bridge across Guanabara Bay and took more than three dozen hostages.

None of the hostages were harmed during the four-hour hijacking, Rio de Janeiro Governor Wilson Witzel told reporters at the scene.

He congratulated the police for an "exemplary performance" in a Twitter post but said he regretted the death of the hijacker.

The bridge that connects state capital Rio with the city of Niteroi across the bay is a major commuter thoroughfare, and the hijacking during the morning rush hour triggered travel chaos in the region.

TV images showed massive traffic jams on the bridge, which was swarming with armed security officials.

The hijacker was armed with a pistol and a knife, said Hans Moreno, a passenger on the bus. Moreno said the hijacker never explained the reasons for his actions. (Reporting by Gabriel Stargardter and Rodrigo Viga Gaier Editing by Chizu Nomiyama and Jonathan Oatis)